The ability to track the precise location and behaviors of experimental animals is highly desirable such as in laboratory animal testing, which is an indispensable part of many areas of biological research and drug discovery. The precision required in the tracking of small animals is often in the centimeter to sub-centimeter scale in order to detect their subtle movements. GPS-based tracking systems, which have been used for larger animals such as dogs and horses, are therefore inadequate to provide the spatial resolution required.
Traditionally, motion tracking of small animals in laboratories is done by beam breaking of infrared light. However, this method suffers from poor spatial resolution, inability to track more than one animal, and in many cases only two-dimensional movement can be detected. Currently tracking of small laboratory animal activities is based primarily on video capture or pressure-sensing technology. Although providing an improved spatial resolution, these methods still suffer many fundamental limitations that greatly restrict their applications. Among those limitations are: (1) inability to track a large number of animals (dozens to hundreds) simultaneously; (2) no long-term tracking is practically feasible without either enormous human labor and time or data storage; (3) animals have to be transported to testing environments where the tracking systems are located, thus subjecting the animals to stress from the transfer and being in novel environments; (4) setting up and executing the tests involves substantial human interaction with the animals, thus adding stress or other unknown factors to the animals; (5) for video tracking, proper tracking is heavily dependent on the lighting conditions of the environment and skin colors of the animals and thus requires frequent contrast adjustments.
In addition to laboratory animals, precise localization and monitoring of movements is much demanded in other subjects. For example, in plant research, extremely high precision is often required to track the minute movement or growth of different parts within a period of time. Video tracking, though being the only assistive method currently used, is of limited applications due to some of the shortcomings listed above.
There are various principles previously published or currently in use for localizing objects utilizing ultrasound as signal carrier.
As described in U.S. Pat. No. 6,317,368, one ultrasound system uses time delays between a transmitter and several receivers to localize the transmitters and utilizes time division multiple access method for sharing the same frequency channel. The drawbacks of using such channel access method are (i) only one transmitter can be tracked at one time slot, which is not suitable for tracking a large number of objects, (ii) the whole system requires strict synchronization, and (iii) interference may be created at a frequency which is directly connected to the time slot length.
Another ultrasound system, such as that described in U.S. Pat. No. 7,283,423, uses time of arrival from a transmitter to one of the many receivers to localize the transmitters and utilizes the method of frequency division multiple access for channel access. The drawbacks of using such channel access method are that the number of objects being tracked at one given time is limited by the partitions of the frequency band and crosstalk may cause interference among frequencies.
More importantly, the spatial resolution provided by the aforementioned systems is limited by the nature of applied techniques, therefore they are not applicable for more precise localization (millimeter range), such as in tracking the movements of laboratory mice or measuring the daily growth rate of plants etc.
Another shortcoming of the aforementioned systems is that the connection between the ultrasonic receivers and the control center is wired for signal transmission. Such system design requires elaborate hardware and infrastructure setup and is often times not feasible to be carried out in well-established and tightly controlled environments such as animal breeding rooms or laboratories for animal testing.
The present invention uses wireless communication technology as positioning and behavioral tracking system and is designed to overcome the aforementioned limitations.